## Description

# What our Mental Math (Add/Subtract) lesson plan includes

Lesson Objectives and Overview: Mental Math (Add/Subtract) teaches students strategies for mentally doing addition and subtraction of two-digit numbers. At the end of the lesson, students will be able to compute basic addition and subtraction with two-digit numbers using mental math strategies. This lesson is for students in 2nd grade and 3rd grade.

### Classroom Procedure

Every lesson plan provides you with a classroom procedure page that outlines a step-by-step guide to follow. You do not have to follow the guide exactly. The guide helps you organize the lesson and details when to hand out worksheets. It also lists information in the blue box that you might find useful. You will find the lesson objectives, state standards, and number of class sessions the lesson should take to complete in this area. In addition, it describes the supplies you will need as well as what and how you need to prepare beforehand. To prepare for this lesson ahead of time, you can copy the handouts and prepare bottle tops with answer for each mat for the lesson activity.

#### Options for Lesson

Included with this lesson is an “Options for Lesson” section that lists a number of suggestions for activities to add to the lesson or substitutions for the ones already in the lesson. One optional addition to this lesson is to create different mats for mental math problems with increasing levels of difficulty. You can also have students play relay games with mental math problems. Finally, you can suggest that students incorporate mental math practice into their morning routines to help solidify the concepts in the lesson.

### Teacher Notes

The teacher notes page includes lines that you can use to add your own notes as you’re preparing for this lesson.

## MENTAL MATH (ADD/SUBTRACT) LESSON PLAN CONTENT PAGES

### Mental Math Addition Strategies

The Mental Math (Add/Subtract) lesson plan includes two content pages. The lesson begins by noting that it’s important to be able to mentally add numbers, and that there are multiple ways to do so. The first method for mentally adding numbers is chaining numbers. This method uses the commutative property of addition. For this method, we pair numbers together in groups of 10 to make mental addition easier. The lesson provides two examples of this method. The first example is the problem 5 + 2 + 1 + 9 + 8. Using this method, we would pair 2 and 8 and pair 1 and 9 to make groups of 10. Once we’ve done this, the new problem is 10 + 10 + 5, and the final sum is 25. Adding two tens and a 5 is easier to do mentally than adding all find addends separately.

The second method for mentally adding numbers is adding in parts. To use this method, we first split all of the numbers into tens and ones. We then add the tens together and the ones together and then add both numbers to get the final sum. The lesson includes two examples; the first is 45 + 30. For this problem, we would split 45 into its tens and ones (40 and 5). The problem is now 40 + 5 + 30. Next, we add just the tens together: 40 + 30 = 70. We then add the tens and ones together: 70 + 5 = 75.

### Mental Math Subtraction Strategies

Next, students learn that, like with addition, being able to mentally subtract is very important! There are multiple ways to make subtracting mentally easier. The first method is to subtract in two parts. For this method, we break numbers apart using the commutative property. The lesson includes two example problems. The first example is 64 – 9. For this problem, we first break the 9 into two parts: 4 and 5. It’s best to break 9 into 4 and 5 because we can subtract a 4 from 64 and get an even 60. 64 – 9 becomes 64 – 4 – 5. 64 – 4 = 60. We then subtract 5 from 60 to get a final answer of 55.

The second method is combining place value (tens and ones). For this method, we break the number being subtracted into tens and ones, then subtract in each part. There are two practice problems that illustrate this method. The first practice problem is 76 – 24. For this problem, we break both numbers into tens and ones. 76 becomes 70 and 6 and 24 becomes 20 and 4. Next, we subtract the tens: 70 – 20 = 50. We then subtract the ones: 6 – 4 = 2. Finally, we combine them to get the final answers, 52. Note that this method doesn’t work for regrouping.

## MENTAL MATH (ADD/SUBTRACT) LESSON PLAN WORKSHEETS

The Mental Math (Add/Subtract) lesson plan includes four worksheets: an activity worksheet, a practice worksheet, a homework assignment, and a quiz. You can refer to the guide on the classroom procedure page to determine when to hand out each worksheet.

### BOTTLE TOPS ACTIVITY WORKSHEET

The activity worksheet asks students to mentally solve 12 problems, placing the matching bottle caps on their mat.

### BREAK UP THE NUMBERS PRACTICE WORKSHEET

For the practice worksheet, students will solve various addition and subtraction problems by breaking up the numbers into different pieces. They will also solve two word problems using mental math, showing their strategy.

### MENTAL MATH HOMEWORK ASSIGNMENT

The homework assignment asks students to complete three short exercises. For the first, they will solve addition problems by adding in parts, breaking the second addend into tens and ones. For the second, they will solve subtraction problems in parts, breaking the second number into two numbers. Finally, they will solve two word problems using mental math, making sure to show their strategy.

### QUIZ

This lesson includes a quiz that you can use test students’ understanding of the lesson material. The quiz asks students to solve six problems, breaking the numbers into parts in their minds to solve using either of the methods covered in this lesson.

### Worksheet Answer Keys

This lesson plan includes answer keys for the practice worksheet, the homework assignment, and the quiz. If you choose to administer the lesson pages to your students via PDF, you will need to save a new file that omits these pages. Otherwise, you can simply print out the applicable pages and keep these as reference for yourself when grading assignments.